Mattress



FIG. 1 is a front perspective view of a mattress in accordance with the present design;

FIG. 2 is a top view thereof;

FIG. 3 is a bottom view thereof;

FIG. 4 is a left view thereof;

FIG. 5 is a right view thereof;

FIG. 6 is a front view thereof; and,

FIG. 7 is a rear view thereof.

The dashed lines in the figures form a part of the claimed design. 

CLAIM We claim the ornamental design for a mattress, as shown and described. 